This invention relates to improvements to the high-pressure mixing apparatuses for mixing reactive chemical components. In particular, the invention relates to a high-pressure mixing method for mixing reactive fluid polymeric components, such as a polyol and an isocyanate to form polyurethane mixtures, in which the action of a plunger or cleaning member is exploited to carry out a self-lubrication and recirculation of a lubricating fluid, to reduce the frictional forces, preventing the polymerisation and adhesion of the reacted mixture to the inner surface of an outlet duct.
The invention also relates to a mixing apparatus or high pressure mixing head, of the aforementioned type, comprising a reciprocable cleaning member or plunger for cleaning the outlet duct by ejecting the resulting mixture, in which the plunger is conformed for scraping and causing a recirculation of a lubricant for the outlet duct.